Internal Carbon Cycling in Tropical Deltaic Sediments

大陆-海洋边缘是地球化学循环强烈的区域，在全球碳循环中起着重要作用。热带活动泥带和三角洲上覆层代表了一类大陆边缘环境，在这些环境中，各种潜在的性质同时结合到一个极端，产生了具有全球意义的大规模成岩反应。这类沉积物中有机物的氧化涉及到碳循环和铁（锰）循环通过硫循环反应的耦合作用，并涉及到化学岩石自养硫化物氧化细菌。因此，两个主要过程负责主题移动沉积物的净CO2生产：碳物质氧化，产生CO2，和化化岩石营养CO2固定，消耗CO2。本项目的主要目标是确定热带缺氧三角洲和流动泥浆环境中这两个碳循环过程的相对重要性，并确定真细菌在其中所起的作用。这一建议是围绕着异养有机氧化和趋化岩石营养二氧化碳固定共同发生在流动泥浆中并有助于这些沉积物产生总体二氧化碳的特定假设设计的。我们建议检查来自沿海法属圭亚那的迁移泥波沉积物，亚马逊河三角洲的下游。为了验证主要的项目假设，我们建议使用放射性示踪剂、微生物学和分子生物学技术的组合来：(I)确定碳循环的反应及其在现场和实验室实验中的速率。使用放射性碳示踪剂，我们将确定有机基质（醋酸盐、藻类生物量）异养氧化和二氧化碳固定和/或产生的相对重要性。为了确定CO2固定是否与自养活性有关，RubisCO I和RubisCO II基因将被扩增和编目。（II）为了模拟趋化营养和异养反应在碳循环中的可能作用，并确定系统对外界干扰的反应，我们将在放射性示踪剂实验和RubisCOI和RubisCOII基因表达的测量中使用代谢抑制剂的组合方法。将估计可能进行循环特定反应的细菌数量，并与沉积细菌总产量的估计进行比较（使用寡核苷酸探针和rRNA测量）。该项目的新颖之处包括确定热带移动沉积物中二氧化碳固定和有机碳氧化的速率，这使我们能够回答这样一个问题：它们在全球范围内是否重要？在缺氧三角洲环境中，化能岩石营养碳固定的作用也将被阐明。在大规模的三角洲环境中，二氧化碳可能被固定，这一事实将对碳循环产生巨大影响。根据参与移动泥带CO2固定的酶（RubisCO I、RubisCO II或CO脱氢酶）的不同，生物量的13C可能会受到影响。我们将探讨二氧化碳固定的机制，并确定RubisCO I或RubisCO II或两者都不介导这种固定（atp依赖性柠檬酸裂解酶或CO脱氢酶）。将确定参与上述生物地球化学过程的微生物，并确定这些微生物的生物活性抑制如何影响整个碳循环。作为该项目更广泛影响的一部分，将培训一名研究生。一名K12教师或一名本科生将参与我们的研究，每年夏天该项目得到资助。项目的结果和进展将通过研究会议、出版物和生物系网站公开发布。对社会的有用性包括了解成岩过程是如何在动态中波中发生的，并允许评估由于人为活动导致的当前和预期的环境变化而导致的加工变化。

0403514ChristoserdovContinent-ocean margins are regions of intense biogeochemical cycling and play a major role in global carbon cycle. Tropical mobile mud belts and delta topset beds represent one class of continental margin environments where these various potential properties simultaneously combine to an extreme, producing massive, diagenetic reactors of global significance. Oxidation of organic matter in this type of sediments involves coupling of the carbon and the Fe(Mn) cycles by reactions of sulfur cycle and involves chemolithoautotrophic sulfide oxidizing bacteria. As a consequence, two principal processes are responsible for the net CO2 production by the topic mobile sediments: oxidation of carbon matter, which produces CO2, and chemolithotrophic CO2 fixation, which consumes CO2. The primary goal of the present proposed project is to establish the relative importance of these two processes of the carbon cycle in tropical suboxic deltaic and mobile mud environments, and to determine the role eubacteria play in them. This proposal is designed around the specific hypothesis that heterotrophic organic oxidation and chemolithotrophic carbon dioxide fixation co-occur in mobile muds and contribute to overall CO2 production by these sediments. We propose to examine deposits from a migrating mud wave in coastal French Guiana, downdrift of the Amazon River delta. To test the primary project hypothesis we propose to use a combination of radiotracer, microbiological and molecular biological techniques to: (I) Identify reactions of the carbon cycle and their rates in the field and laboratory experiments. Using radioactive carbon tracers, we will determine the relative importance of heterotrophic oxidation of organic substrates (acetate, algal biomass) and CO2 fixation and/or production. To determine whether CO2 fixation is connected with autotrophic activity the genes for RubisCO I and RubisCO II will be amplified and cataloged. (II) To model possible role of chemolithotrophic and heterotrophic reactions in the carbon cycle and ascertain responses of the system to outside disturbances, we will use a combined approach of metabolic inhibitors in radiotracer experiments and measurements of RubisCOI and RubisCOII gene expression. The number of bacteria potentially able to carry out specific reactions of the cycle will be estimated and compared with estimates of total sedimentary bacterial production (using oligonucleotide probes and measurement of rRNA). The novelty of the project include determination of the rate of CO2 fixation and organic carbon oxidation in tropical mobile sediments, which allow us to answer the question: Are they significant on a global scale?. The role of chemolithotrophic carbon fixation in suboxic deltaic environments will also be elucidated. The fact that CO2 might be fixed in massive deltaic environments would have tremendous impact on the carbon cycle. Depending on the enzymes participating in CO2 fixation in mobile mud belts (RubisCO I, RubisCO II or CO dehydrogenase), 13C of biomass may be affected. We will address the mechanism by which CO2 is fixed and determine whether RubisCO I or RubisCO II or neither (ATP-dependent citrate lyase or CO dehydrogenase) mediate this fixation. Microorganisms involved in the above described biogeochemical processes will be identified and how the inhibition of biological activity of these microorganisms affects the overall carbon cycle will be ascertained. As a part of broader impacts of the project, one graduate student will be trained. One K12 teacher or an undergraduate student will be involved in our research every summer that the project is funded. Results and progress on project will be publicly disseminated through research meeting, publications and the Department of Biology Web site. Usefulness for the society includes the understanding of how the diagenetic processing is occurring in the dynamic mid wave and allowing to evaluate changes in the processing due to present and anticipated changes in the environment as a result of anthropogenic activity.